US 2006/0108618 A1 discloses a CMOS image sensor having buried channel MOS-transistors, wherein the CMOS image sensor includes a photo-converting device and a source follower transistor. Thereby, the photo-converting device generates a current signal and changes a voltage of a floating node in response to energy of an incident light.
It may be known to form a bipolar transistor in a MOS semiconductor process. Thereby, a p+ active area within an Nwell-region (n-) may form the emitter, the Nwell itself forms the base and the low doped substrate (p-) forms the connector (in the case of a pnp type bipolar transistor). It may also be known to use this kind of bipolar transistor as a photo-transistor in which case the base contact or base terminal is removed so that the Nwell is floating (i.e. has no defined electric potential). Under the influence of light impinging in this region, electrical charges may be generated within the Nwell and a current may flow between the emitter and the collector depending on their voltage difference, the wavelength and the intensity of the impinging light.
However, it has been observed that this photo-transistor has several disadvantages. First of all, the geometry, especially the width of the base may not be well controlled. Further, this photo-transistor may have a low current gain. Furthermore, this kind of photo-transistor has a strong temperature dependency, i.e. the current between the emitter and the collector heavily or strongly depends on the temperature which may hamper the quality of the signal which should ideally be linearly dependent on the light intensity. In particular, due to the high temperature dependency, the linearity of the sensor cannot be ensured. The same disadvantages have been observed for the complementary transistor, i.e. the npn type bipolar transistor configured as a photo-transistor.
There may be a need for an arrangement for registering or sensing light (and in particular providing an output signal being essentially linearly dependent on the light intensity), wherein at least some of the above-mentioned disadvantages are reduced or even overcome. In particular, there may be a need for an arrangement for registering light which provides a reliable light detection which can be manufactured in an integrated manner, such as to serve also as a light sensor within a chip card.
The above need is satisfied by the subject-matter of the independent claim which is directed to an arrangement for registering light. The dependent claims specify particular embodiments of the present invention.